Semiconductor arrangements formed in a wafer, such as for example memory devices, logic device, processors and others, generally have a plurality of metallization levels that are electrically connected to one another via metal contacts. Lithography processes in combination with subsequent RIE (Reactive Ion Etching) or similar processes are used to produce metal contacts of this type. Therefore, the lithography processes produce etching masks on the substrate, so that contact holes can then be etched into the substrate through the etching masks by means of RIE, extending down as far as the next metallization level.
In principle, it is possible for the contact holes to be completely filled with tungsten by means of an M-CVD (modified chemical vapor deposition) process. However, this requires prior deposition of TiN, and then a polishing step (CMP) after the tungsten CVD process. Drawbacks of filling the contact holes with tungsten are the relatively high contact resistance and the technological outlay.
It would be more advantageous for the contact holes to be filled with aluminum. Aluminum contacts of this type would have a significantly lower contact resistance. Various processes have been proposed and used in practice for the production of aluminum contacts of this type.
By way of example, this has been done by Lee, et al. (J. M. Lee, B. H. Kim, J. Y. Yun, M. B. Lee, G. H. Choi, Y. W. Park, H. K. Shin, S. I. Lee, J. T. Moon, “A Noble Metallization Process Using Preferential Metal Deposition (PMD)—Aluminum with Methylpyrroridine Alane (MPA),” Proceedings of the International Interconnect Conference, Jun. 4–6, 2001) by depositing a very thin PVD (physical vapor deposition) layer of MPA at the surface (not in the contact hole). A subsequent CVD aluminum layer then grows only in the contact hole. Finally, the contact hole is filled using a PVD reflow process at moderate temperatures.
Since the CVD-Al layer, which is in this case required to flow, is not on a planar surface, its height is not increased by the roughness of the reflow aluminum. The drawback of this process, however, is that it is a very complex procedure that requires various process steps that take place very slowly.
Another process is described by Yun, et al. (J. H. Yun, K. Y. Kim, S. G. Jin, K. R. Yoon, S. H. Lee, I. C. Ryu, S. K. Park, “Submicron Via-Hole Filling using Al Low-Pressure Seed Process,” Jpn. J. Appl. Phys. Vol. 40 (2001) pp. 5105–5108, Part I, No. 8, August 2001). This process uses a commercially available coating installation produced by Applied Materials with the process intended for the installation to fill contact holes in a wafer with aluminum.
In this case, a 400 nm thick aluminum nucleation layer is deposited in vacuo in a separate chamber (long throw technique) while the wafer is on a cooled electrostatic chuck (ESC). The actual filling process is then carried out at temperatures of 450° C. in a further aluminum PVD chamber in vacuo after a heating time of 120 s, with a very low deposition rate at a sputtering power of 2 kW. This means that the filling of the contact holes (vias) with aluminum is carried out in two steps in different vacuum chambers, with a handler being used to transfer the wafers from chamber to chamber.
A handler is to be understood as meaning a device for transferring wafers from a magazine of a loading station (e.g., a FOUP or Front Opening Unified Pod) into a chamber and from the latter into further chambers and ultimately back into a further magazine of the loading station. This handler is arranged in an evacuable transfer chamber located between the processing chambers.
The drawback in this case is that two different aluminum coating chambers are required, with the associated increase in time required to transfer the wafers and the need for the required process parameters in the corresponding chamber to be reset after each transfer, as well as the very slow aluminum flow process.